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Патент USA US2112549

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March 29, 1938-
E. P. G. WRIGHT ET AL
‘TELEPHONE SYSTEM
2,112,549
Filed June 11, 1936
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'WENTORS '
GZCIHARTLB’
ATTORNEY
March 29,. 193.8.
‘E. P. G. WRIGHT a? AL
2,112,549
TELEPHONE SYSTEM
Filed June 11, 1936
<I<
4 Sheets-Sheet 4
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By G.C.HAR7ZEV -
' wgegua
ATTORNEY
'
2,112,549.
Patented Mar. 29, 1938
UNITED STATES PATENT OFFICE
2,112,549
TELEPHONE SYSTEM
Esmond P. G. Wright and George C. Hartley,
London, England, assignors’to Western Elec
tric Company, Incorporated, New York, N. Y.,
a corporation of New York
'
Application June 11, 1936, Serial No. 84,640
In Great Britain June 21, 1935
15 Claims.
This invention relates to telephone systems and
more particularly, though not exclusively, to
equipment for use in setting up long-distance or
toll connections.
The nature of the invention will be understood
from the following description of certain em
bodiments thereof.
It is intended to provide a combined line and
recording (C. L. R.) toll service entirely without
10 plugs and cords. Each position is equipped with
links having talking and monitoring keys and
supervisory lamps, but the usual plugs are re
placed by automatic switching apparatus. The
switching apparatus can be controlled either by
15 dials on the operator’s positions or by key sender
equipment. Access is provided by means of the
automatic switches to all toll routes, to the local
exchange equipment, and to miscellaneous cir
cuits such as test desk information and enquiry
20
positions, etc.
Types of positions
There are two principal types of positions,
namely inward and outward. The link circuits
of the inward positions are connected at one end
to trunk line ?nders which can search for and
pick up incoming calls, and at the other end to
toll ?rst selectors which are the ?rst switches in
the automatic switch train giving access to the
various
toll routes and the local exchanges. Each
3O
operator has up to ?fteen inward links on her
position, each one having a listening key and
(Cl. 179—2'7)
required, the link may be used for point-to-point
Work, or for the establishment of delayed calls.
It is likely that this facility will be of considerable
use in enabling the operator to release the calling
side of the link and reverse the call should the 5
calling party for any reason have become discon
nected during the time in which the operator ‘has
been waiting for the forward connection.
Method of operation
scribed later on, the method of operation on var
ious classes of call is as follows:
(A). Inward calZs.—-An inward call arriving on
a toll line circuit establishes a calling condition to 15
the.allotters which control the movement of the '
trunk line ?nders.
These allotters will select a
suitable link circuit for handling the call, and will
cause the associated ?nder to search for and seize
the toll line circuit. The principle of distribution '20
governing the movement of the allottersis that
calls shall be distributed to the various positions
in rotation, except in so far as this is rendered
impossible either by reason of there being no free
links on a given position or if the position due to 25
receive the next call is still testing busy owing
to the operator not having cleared the sender
from the preceding call. This latter condition
may, of course, arise if the operator has difliculty
in dealing with a call such, for instance, as a. per- 30
sonal call in which di?iculty is experienced in lo
cating the wanted party.
monitoring key, calling and called supervisory
When the inward link seizes a toll line circuit,
lamps, and a busy lamp. The associated posi
35 tion circuit contains the various keys required to
control the completion and supervision of the con
nection, including keys for ringing both ways,
splitting and releasing either way, together with
the digit keys required to control the key senders.
The outward positions are arranged to pro
a ?icker condition is established on the calling
vide C. L. R. outward services, and also to act as
toll or point-to-point positions.
They are ?tted
with two types of link circuits; the ?rst is con
nected to a ?nder at one end, which searches for
45 incoming calls on the record circuits, and at the
other end to a toll ?rst selector; while the second
kind of link is connected at both ends to toll ?rst
selectors via selector ?nders which are introduced
to cut down the number of ?rst selectors required.
The C. L. R. links have a special feature where
by the ?rst level of the ?nder is connected, not to
incoming record circuits, but to toll ?rst selectors.
Normally, the ?nder will not search over this level
10
Apart from the delayed search facility de
supervisory lamp. The operator will answer by
throwing her listening key, and this process will
cause the sender ?nder associated with the posi
tion to pick up a free sender. At the same time,
the link circuit is connected to the operator’s po
sition circuit. The operator will ascertain the
particulars of the required connection, and will
immediately set up the required digits on her key
strip. The sender will then transmit the required
digits to the automatic selecting equipment, and
in the case of a call terminating locally in an
automatic exchange, this will actually give con
nection to the wanted subscriber. In the case of
a through call to another toll line, the automatic
switchgear will simply select the toll line andthe
subsequent ringing and supervisory work will be
as for standard toll practice.
During the time that the sender is transmitting
the required digits, it connects itself direct to the
but can be made to do so under control of a key
link via a by-path circuit so that the position cir
in the operator's position circuit so that, when
cuit is rendered available for the monitoring and
50
55
2
2,112,549
supervisory work on existing calls, including the
congested route.
clearing of any which have been completed. As
long, however, as the sender remains connected
to the link, the position is rendered busy to fur
ther incoming calls.
special arrangements for the group selector cir
cuits which search for a free toll line. The selec—
To give toll line ringing, subscriber’s ringing, or
any similar signals, the operator throws the lis
tening key of the required link, and subsequently
This di?iculty is avoided by
tors of these circuits are ?tted with an additional
wiper, the bank contacts associated with which
aretaken to a group congestion circuit and when
a toll line. selector arrivesat the beginning of a
release an established connection, the link circuit
listening key is thrown, followed by the link re—'
lease key, it being assumed that the normal rou
tine for clearing the tolljline. to the other op
erator has previously been carried. out. The toll
group, before commencing a search it makes a
test on this outlet for the special condition from
the congestion circuit. If no toll line is available, 10
this. condition will not be forthcoming, and the
selector will refuse to, search, but will issue busy
?ash to the operator. The operator may now
restore her listening key in order to carry on
15 line signal is received as a' ?icker signal on the
with further calls. The busy ?ash will stop, but 15
the appropriate keys of the position circuit.
To .
supervisory lamp and this ?icker condition in the
the link busy lamp will remain alight. When a
toll line circuit is automatica-ll-‘y'removed by the ' toll line becomes free, the appropriate test condi
throwing of the associated listening key. In tion is restored to the control bank contacts,
order to enable the operator to correct errors, or 1 and this will cause the group selector to transmit
20
to ,re-route ,calls in, cases _of di?iculty, a forward
releaseykey'isprovided which‘re'leases the forward
train but not they entire link; the operator may
then; throw a» key tore-introduce the vsender and
establish’ the call afresh.
25
‘
'
test arrangements aremade so that in the ‘event
of two operators simultaneously attempting to
seize the only’ available, junction, only one selector
the customary 'docket'ing and'timing operations,
will commence to search and the other will pro
and will in consequence be unable» to handle the
ceed to transmit the ?icker waiting signal again.
same amount of tra?lc. As a consequence of this,
Delayed ‘Search may be provided on a non-nu
theudistribution' rscheme7di?ers from that'ifor
merical forwardly hunting switch accessible from
inward‘calls‘in that aneperatqr will‘ signify her
willingness tomaccept a call by throwingxthe key
whereupon thelallotters will steer the calls to the
positions thus’ indicated: The C‘. L. R. links are
?tted with a device to enable them‘_ to be used
position is provided with back and front release
keys as well as a‘ key 'torelease the entire link‘.
The operator can, therefore, when required, re
leasev the ?nder from a record circuit and by
throwing a; special vkey cause the‘ ?nder to select
a toll ?rst selector, and by the use of her key
sender can reverse the'call to any desired ter
45 minationt,
(C'). Point-to-point calla-'I'hésé-are
1..
‘r delayed
calls built up in accordance with dockets, and
they .will normally _use the double “ended links
provided for this purpose.‘ The operator will con
necther key sender to the back, and front ends
of the cord in turn, and will establish thereby
a connection to the wanted parties or distant
operators as the case may be.
G’roup display lamps
55
to
this will cause the toll‘ line selector to search over
the group and select a free line. Special double
' '(-B)-.' Outward callS'.--The operating procedure
asHpoint-to-point links and, in' consequence, the
so
connection, she will throw the listening key and
on outward calls is essentially'the same‘ except
that'7the5 operator will be required tof perform
35
a ?icker signal to the voperator. If she decides to 20
avail herself of the opportunity to complete the
Both classes of positions are ‘provided with a
group of lamps to indicate the groupor route of
the incoming call. These lamps’ are lighted from
an. additional bank of the line ?nder,_and,in order
to avoid excessive splitting of the multiple,’ this
bank is multipled over a, number of positions.
This would normally result in confusion between
the indications required by. the various positions,
and to avoid this a ?icker‘indication is given,,the
various positions being connected‘ in turn, each
for a'short period. The lighting of these lamps
is controlled by. the keys on the position, so‘ vthat
the ?icker control relaysneed not operate except
when the operator requires the display.
Delayed search ‘
Oneofthe major di?iculties in securing em
cient working of a .C. L. B, toll board is due to
30
a group selector instead of on the ‘group selector
itself.
The group‘ congestion circuit which con— ‘
t'rols this operation is arranged for. special sig
naling on both-way routes/so that when. calls are
35
Waiting , on toll line. selectors at each end of
a both-way group, the congestion circuits will
allow them to be released in rotation in a sequence
dependent on the time for which calls have been
waiting at each end.
40
Special arrangement of senders
The ‘sender circuits are arranged to accept the
necessary code digits for the selection of an
outgoing route, and also the numerical digits re 45
quired for establishing aflocal connection, or con
nection to- a route which employs through dial
ing. The sender will normally send the complete
storage, but in the event ,of the toll line selector
on an out-dialing call failing to obtain im
50
mediategaccess to a free junction, the sender, will
release without transmitting the numericals.
When the operator, after the delayed search op
eration, eventually succeeds in obtaining, a toll’
line, she will reset the numericals in the sender, 55
using a dummy code , combination whichv the
sender will not retransmit.
7
Another object ‘of the invention is to provide
means to permit a both-way junction to be used
in such a manner that the period of delay is 60
maintained approximately equal ‘for calls in each
direction.
It will be understood that where the
number of junctions isrelatively small the device
willrcontrol all the circuits but that in cases
where the number of junctions is greater, ar 65
rangements can be made to divide the available
junctions into three groups, the ?rst operating
only in one direction, the second operating in the
reverse direction and thethird operating in either
direction, according to the circumstances of. the 70
tra?ic. In the past it has been the practice for
this control to be exercised by the operators at
the terminations of the junctions.
the time taken by the operators in making re
On long-distance circuits, for which delay
peated attempts to establish connections on a
working has to be introduced frequently, it is a 75
2,112,549
common practice for the operators to pass a
and on seizure the negative‘ and. positive wires
number of calls in one direction and then a
a and b are looped causing the operation of
relay A. Relay A closes a possible circuit for the
relay P leading to a wiper, the bank contact of
which, in the home position, is connected to a
source of battery potential if any of the outlets
number of calls in the other direction, without
paying particular attention to the waiting load
of tra?ic at either end.
I
With more recent methods of toll switching it
is becoming a practice to indicate to the opera
tor one free junction in each group appearing on
' her position, and should all junctions be simul
10 taneously in use, the particular one which be
comes free ?rst will be immediately indicated at‘
both ends. Furthermore, no pro-vision is made to
prevent the same junction being indicated at
both ends even when more than one junction is
free.
'
‘
With C. L. R. working, a call is set up directly
if a junction is available within, say, thirty
seconds, but if a junction is not available in that
time, the calling party is asked to hang up and a
ticket is made out and passed to a “delayed call”
position. In the systems employing call storage,
however, it is the practice to encourage the oper
ators to await a circuit becoming free for a longer
time, and it will be understood that if there'are
a number of calls waiting at each end of the
junction there is a considerable danger that the
junction will be seized at both ends simultane
ously and the calls mutilated.
'
If toll dialing is employed it is important that
such collisions should be avoided, and the pres
fromthe switch are available.
This source of
potential is 'su?icient to cause the operation of
relay P which is a relay of the two-winding type
and which is adapted to short-circuit one wind 10
ing on its operation in order to reduce the po
tential on the bank contact after operation. Re
lay A also closes a circuit for relay C which also
has two windings, one of which is normally short
circuited, in which circumstances the relay C is 15
slow to operate. If the relay P does operate
it will open the circuit of relay C and close the
circuit of relay L, which will look over its own
make-before-break contacts. Relay L closes the
driving circuit for the switch from ground con
nected to the bank contacts and the switch will
continue to run through its interrupter contacts
until it reaches an outlet not marked busy. At
this point the relay K operates in series with the
rotary magnet and switches the incoming leads "25
through to the outlet.
The relay K is main
tained operated on the third wire. If all the
outlets are engaged the relay P fails to operate
and the relay C operates, connecting a flashing
signal from lead FL to the fourth wire d which
will cause a supervisory lamp at the operator’s
ent invention also provides means to control the
position to flash intermittently. Relay C also
direction from which calls should be accepted at
the time of congestion. To accomplish this a I connects the high resistance relay HR in series
with relay P to the group control wiper so that
recording device is associated with each end of a
when source of potential is connected, indicat 35
group of junctions and a record is maintained of
ing that one of the outlets has become free,
the product of the number of calls and the delay.
the relay I-IR only will'operaten Relay HR in
It may happen that if there is a preponderance
operating removes the flash. from the (2 wire
of calls in one direction, a single call in the re
which is now connected to a flicker signal in
verse direction will have di?iculty in being han
series with the second winding of relay C back 40
lie dled in its correct turn. To compensate for this to
the operator. The original operating circuit
possibility a further feature of this invention
of relay C is now switched over to an interrupted
provides means whereby after a number of calls
battery which is so timed in relation to the
in one direction preference is given to a call wait
?icker signal that the relay is alternately main
ing in the reverse direction, and as the number
tained operated over one winding and then the 45
“is of successive calls in one direction increases the other.
When the operator wishes to commence
preference is also increased, tending to reverse
the searching operation, the circuit over the
direction.
'
‘fourth wire is opened, causing relay C to release.
In the accompanying drawings;
The low resistance circuit for relay P is recon
Fig. 1 shows the circuit of a non-numerical
nected and when the relay P operates the switch 50
'50 junction selector adapted for delayed calls;
hunts as already described. If two operators
Fig. 2 shows the circuit of a two-motion junc
attempt to take a free outlet simultaneously only
tion selector;
'
one P relay will operate, but in the other circuit
Fig. 3 represents, in schematic form, the cir
relay HR will release, relay C will reoperate and
cuits associated with both ends of a both-way
?ashing signal will be reconnected to the cl wire. 55
junction group arranged to allot a junction fall
When a further outlet becomes free the relay
ing idle to the end at which congestion is worse;
HR will operate again and the operator can
Fig. 4 shows the relevant portion of a non-nu
merical trunk selector, of the kind shown in make a further attempt in response to ?icker.
Fig. 2 shows the circuit of a two-motion sew
full in Fig. 1;
lector which is arranged to be set by either one 60
60 Fig. 5 shows a direction delay recorder; as
sociated in multiple with all non-numerical trunk or two digits according‘ as the group required
'?lls a level or uses only part of a level. Relay
selectors of a group;
C, not shown, is arranged in the normal manner
Fig. 6 represents a delay counter circuit, as
sociated with all the direction delay recorders; to operate with each impulse. This relay is slow
Fig. 7 represents a both-way trunk line circuit to release and controls the release relay CC which 65
65
is also slow to release. When relay C releases
accessible from the trunk selector;
'
at the end of the ?rst (or second) digit a circuit
Fig. 8 is an association circuit for connecting
together a direction delay recorder and a trunk is closed through the operating contacts of relay
CC to the congestion relay P and if ‘the relay‘ P
line circuit as the latter becomes free;
operates to battery via the group congestion cir- "
Fig. 9 is a direction compensator and is indi
vidual to the direction delay recorder of Fig. 5. cuit GCC, the drive circuit of the rotary magnet
Fig. 1 shows a non-numerical switch, the vRM, in series with left-hand winding of relay
searching operation of which is in part con
CC, is completed via wiper wB to earth on all
trolled by an operator. The circuit is taken into the contacts of the group except the last and
selection of an idle outlet takes place in‘kno-‘wn
use from the bank contacts of a selector level
2,112,549
'manner." When the switching relay H '(not
shown) operates its contacts hI switch through
lead d. If the relay P fails to operate before the
relay‘ ‘CC releases, the circuit will be completed.
for the relay BF through the contacts s02, hr2,
cI, pl, ml to earth. ‘Relay BF'connects the ?ash
jing lead FLA to the relay FL which in turn con
meets the relay SC intermittently to the fourth
wire, thereby giving a ?ashing signal to the op
10 erator.
When the operator restores her listening
key, relayv SC operates and locks, releasing BF
so that busy ?ash is removed. Relay CC, in its
normal position, also closes the circuit for the
high resistance relay HR to the group control
contact in series with P. When an outlet becomes
free relay HR alone operates and switches over
the circuit FL at hrl to the ?icker ground via
FLI thereby causing av quicker train of impulses
to be sent back over the fourth wire to ?icker
v20 the operator’s lamp.
During these interruptions
the circuit for the relay SC is maintained oper
ated over its locking circuit. ‘When the operator
wishes the switch to attempt a search, the cir
ciiit‘ of the relay SC is opened or high resistance
:25 is‘inserted therein by throwing the listening key
and the relay SC recloses the circuit for the relay
BF. With both BF and HR operated, the relay
CC reoperates via hT5, M3 and allows a further
test to be made by the relay P; The circuit of
the relay HR is opened by the‘ relay CC and if
relay P fails to operate before CC also releases,
the ?ashing signal is reintroduced as already
described.
'
The incoming and outgoing circuits are now
ready to signal the amount of congestion recorded
to each other. "If calls are waiting at the in
coming end, a ?rst “congestion” pulse of 'Y fre
quency will be sent, and at the same time, the
switch R3 of the incoming DR will be stepped
forward atleast one step. At the outgoing end,
on receipt of this pulse, a Y pulse is sent back and
the corresponding R3 is also stepped, Originally,
whenno congestion existed, R2 and R3 of DR 10
were both at normal. R2 has been stepped for
ward over a number of contacts determinedv by
the number of TS circuits of the group awaiting
a free junction, and by the length of time these
TS circuits have been in the waiting condition. .15
RI takes one step per half-second and is a ?fty
point switch, and. therefore R2 has taken one
step per waiting TS every twenty-?ve seconds
R3, when stepped as JC sends a Y “congestion”
pulse, takes at least one step to catch up with R2. .20
R3 takes four steps per Y congestion pulse'nor
mally, but is controlled by DRC to take only two
stepsor one step if the other exchange has taken
the last two, or three, junctions falling free re
spectively.
equipment at both ends of a both-way junction
group, an operator setting up a call in_ a wanted
direction, is connected via a group selector GS to
a non-numerical trunk selector TS, which is of
the kind shown in Fig.’ 1 and is adapted to give
access to an idle both-way junction circuit J C.
If all the outlets from TS are busy, connection
is made to a direction delay recorder DR associ
ated in multiple with all TS circuits giving access
to the same group of toll junctions or trunks.
:45 Associated with all the DR circuits is a delay
counter circuit DLC comprising a switch RI
which is stepped round at a given speed whenever
congestion conditions exist and has a'position in
dividual to each TS circuit. During each revo
"50 lution of switch RI, a switch R2 of each DR is
given at least one step for each of its associated
TS circuits awaiting a free outlet. The number
of steps taken by R2 in this way is determined
by a relay DP individual to DR. 'The compen
sator DRC comprises a switch R5 which records
the number of times those junctions of the group
in question, on becoming free, are taken into use
-
.25
exchange Y pulses until switch R3 at one end
catches up with its-R2, when no more Y pulses
Will be sent from that end, and the "other end
.still having congestion recorded, and receiving no 30
further Y pulse, allows the TS circuits to flicker
the operators‘ to inform them that aijunction' is
available.
Referring now to Fig. 3,’ which represents the‘
~
The incoming and outgoing ends continue to‘
'
'
~
’
'
Congestion records at both ends willthen be
35
built up ‘ again.
It will be seen that the end which has not taken
the last two or more junctions, counts off its con
gestion record by means of switch R3 at a much
slower rate than the other end, and therefore is
more likely to get an available junction. DRC 40
of course allows switch R3 to resume its normal
stepping rate after a junction has been taken,
from that end.
If no congestion is. recorded at the outgoing
end, the return Y pulse therefrom, before con-ges 45
tion signaling begins, is replaced by an X pulse,
in response to which the incoming end takes the
junction immediately.
'
Referring now to Fig. 4, only a small portion of
the non-numerical trunk selector previously de 50
scribed with reference to Fig. 1 is shown. The
selector is arranged to pass back a ?ashing sig
nal to the operator indicating that all the trunk
‘circuits are engaged. Relay C remains operated
during the waiting period. Relay HR is connect 55
ed to a wiper of the switch by C and will oper
ate as soon as a trunk becomes available.1"The
consecutively at the far end, and accordingly
varies the rate of stepping of a second switch R3
operation of the relay HR will release 0. Relay
HR removes the ?ashing signal and substitutes
60 of DR for a purpose which will be explained
a ?icker thereby indicating to the operator that 60
shortly. The circuits JC of a group are adapted ‘a trunk line is available. The fact that‘ relay C
to be individually connected to the corresponding is operated in any one trunk selector circuit indi
DR by an associated circuit AC. This connection cates that an. operator is waiting for a trunk line.
is automatically made each time a junction falls -It follows that an indication of the tra?ic wait-‘
65 free irrespective of the existence of congestion ing in any direction can be obtained by measur 65
conditions in the group. Each JC comprises a ing the number of C relays which are operated
switch R4.
'
When a junction falls free, the JC circuits at
both ends are connected to their DR circuits and
the switch R4 at the outgoing end for the call
just terminated is stepped, causing pulses of two
different frequencies X, Y to be sent consecutive
ly. On receipt of this signal R4, at the incoming
end, sends back a pulse of the Y frequency and the
75 outgoing R4 returnsa further Y pulse.
simultaneously and the time period during which
they remain operated. ’ This measurement must
be made independently for each direction and
the direction delay recorder DR is, therefore, as- -
sociated only with a group of TS circuits giving,
access to junctions in one direction only.
The actual measurement is controlled by the
delay counter Fig. ‘6 which-‘may be common to’ a
70
,
2,112,549
number‘ of directions. Detailed operation takes
place as follows:
.
Relay C in the non-numerical trunk selector
Fig. 4 connects ground through a decoupling re
sistance to relay ST of the direction delay re
corder, Fig. 5, which in operating closes the ob
vious circuit for a congestion meter CM indicat
ing the number of occasions on which all trunk
lines are engaged. It also closes the obvious cir
cuit for the relay CST of the delay counter Fig. 6.
Relay CST in operating connects the magnet
RMI of the switch Rl to a half-second pulse
supply causing the wipers of the switch to step
forward one step every half second.
15
‘
Two wipers Tm] I, Tml2 are connected to
gether, one set of bank contacts being connected
individually to C contacts of the trunk selectors,
the other set of bank contacts being strapped to
gether according to direction and connected to
relays DP in the corresponding direction delay
recorders, Fig. 5.
.
Every time the wipers of the switch RI pass
over contacts corresponding to a trunk selector
TS of the group associated with DR, Fig. 5, in
25 the waiting condition, a ground connection will
be passed to the relay DP in the delay recorder.
Relay DP in operating closes the obvious circuit
for magnet RM2 of the switch R2, which ad
vances its wipers accordingly.’
The switch R2 has only one level of contacts
which are connected to a corresponding set of
contacts in the switch R3, which also forms a
part of the direction delay recorder. The switch
R3 is advanced only when a trunk circuit be
35 comes free and it is the function of the switches
R2 and R3 to count off between them the amount
of delay which has been storedsince the last
trunk circuit became free.
7
Relay PC which is connected to the wiper rm3l
40 is arranged to operate when the switches R3 and
R2 are approximately in phase.
The wipers of the switch R3 are advanced in
stages until the relay PC eventually operates
indicating that the switch R3 has caught up the
switch R2.
per trunk line circuit and one of these relays and
v its contacts are shown on Fig. 7.
The number of steps of the switch
R3 comprising the stage may be varied by ‘the
compensator, Fig. 9, as described subsequently
according to the circumstances.
When a trunk circuit is about to fall free be
50 cause the call for which it has been used is
ended, the release is made dependent upon the
direction delay recorder and for this reason the
both-way trunk line circuit Fig. 7 must be as
sociated with the recorder. This association is
performed by a group of relays K shown in Fig. 8,
the connecting function of one of the K relays
being shown in Fig. 7.
It will be appreciated that due to the releas
ing times of relays and the possible differences
60 in exchange voltages the both-way circuit may
not tend to become free simultaneously at both
ends, and should it happen that two junctions
of a group become free at approximately the
The pairs of terminals AKI, AK2; AK3, AK4,
Figs. 7 and 8, are particular to different junc
tion circuits JC. A potential is connected to
terminal AKI, for instance, when the correspond;
ing trunk line is about to release after com
pleting an outgoing call, and a similar potential
is placed on the terminal AK2 when the same cir
cuit JC is about to release after receiving an 10
incoming call. At one end of the trunk linethe
terminals AK! and AK2 are connected together,
but at the other end they are wired separately
in order to avoid cross connections.
When a ground potential is connected to: a 15'
point such as AK3, Fig. 8, at the end of an out
going call, the relay K2 will operate through con
tacts MI, 1092, k22,—kw| to battery potential
through relay KY. Relay K2 in operating closes
its make-before-br‘eak contacts making itself in 20
dependent of the break contact 71:22. Ground
potential now being placed on terminals AKI or
AK5 at the termination of other outgoing calls
will not cause the operation of the relay KI or
K3 because the operating circuit is opened at the 25
contacts 7022.
When the pairs of terminals AKI and AK2,
AK3 and AK4, etc. are connected together, and
the K relays, Fig. 8, need have no‘ right-hand
windings, only one K relay can be operated at a 30
time and this relay will remain operated until
the trunk line circuit removes the ground poten
tial.
When the corresponding terminals are not
wired together but wired separately, the second 35
terminal is Wired through a second Winding of the
K relay and through a relay KW to- the battery
potential through relay KY. With this arrange
ment a K relay can become operated on its
second winding even if another K relay is al 40
ready operated on its ?rst winding. Further
more, the operation of the relay KW in series
with said K relay will open the circuits of the
?rst windings of all K relays so that any K relay,
which was previously operated via an outgoing 45
terminal, is caused to release.
The K relay at the “incoming” end of a-junc
tion about to come free cannot operate until a
signal has been received from the outgoing end
after the latter has been connected to its DR. 50
It will be seen that with this arrangement if two
trunk lines which have been used in different
directions are released simultaneously and both
outgoing ends make association with their cor
responding direction delay recorders and, in 55
consequence, initiate the releasing signals, a sec
ond K relay will be operated over its second
winding at the one end to disassociate the delay.
recorder at that ‘end from the toll line to‘ which
it is connected and reassociate it with the toll 60
line which has received an incoming signal.
Turning now to Fig. 7, the relay A is bridged
across the conversational leads from the local
subscriber and is designedv to operate so long as
same time, the associating relays may be caused
to operate in such a way that the direction delay
recorders at opposite ends become individually
connected to different junctions and are unable
the callingsubscriber’s receiver is off the hook. 65
The outgoing conversational leads are not shown.
Relay A operates B, which is of the slow to re
to signal to one another. In order toavoid con
fusion arising in this way, one of the two termi
up so that the toll line circuit is not. automati
nations acts slightly diiferent from the other, it
being adapted to cancel the ?rst association and
lease type.
Relay C then operates and locks
cally released when the calling subscriber clears. 70
make a second association when the conditions
Considering ?rst the case in which the trunk
line circuit is used for an outgoing call. The
indicate that the direction delay recorders have
been associated with different trunk lines.
The relays KI, K2, K3, etc., are provided one
circuit for the magnet RM4 of switch R4
through its interrupter springs, the ?rst bank 76
operation of relay B closes at contacts b-l the
6
2,112,549
QQntact and wiperrm? causing the switch to
advance to position 2. The. relay SC isoperated
responding’ terminal of the both-way trunk cir
cuit, through k2, and rm42 to magnet RM4;
.(Yl?jCOIlt?Cl; a2 of relay A) on all outgoing calls
and the contact 30! closes a circuit for magnet
RlVI4;"via its interrupter springs, sol, bank con
tacts, wiper rm43 to ground. This circuit is
maintained until wiper rm44 reaches its ?rst
contacts, which is the twenty-sixth position of
the switch. The switch remains in this position
This signal causes the switch R4 to advance a
step and in the following position 35 a circuit is
reestablished for the relay FXY which again ap
plied Y pulse over the trunk line. Switch R4
does not remain for any length of time .in this
position because the circuit is at once closed
through the wiper rm42 which causes the wipers
is during the course of conversation but at the
completion of’ conversation when the relay
B/releases the circuit for the magnet RM4 is
completed through wiper rm42, the break con
tact b2, the contacts gl and the wiper rm44 to
ground. The switch advances its wipers one
step to position 21 in which position ground is
connected to the terminal AKI through con
tacts b3, roll, 302 and wiper rm48. If the direc
tion delay recorder is not already associated with
20 a trunk line circuit, the relay K will operate and.
close at contact kl the circuit through the
wiper rm42 for the magnet RM4, which ad
vances the switch to position 28. In this posi
tion the toll. line circuit sends the initial re
25 lease signal to the distant end. It will be under
stood that the signaling over the toll line may
be vcarried out in a number of di?erent ways,
‘e. g. by the use of two or more voice frequencies
placed on the line or by the use of a single fre
30 quency of various duration or by means of direct
current signals. In this description it has been
assumed that signaling is undertaken by means
of two voice frequencies, but the sources of fre
quencies and their connections to the outgoing
junction leads are not shown as they may be
of any known type. When the switch R4
reaches position 28, that is, the third position in
banks rm42, 44, 46 and 48, the circuit is closed
for the relay FX through wiper rm46 contacts
40 kl I, 302, rcl, b3.
FX in operating, connects the
X frequency to the outgoing line. In position
"the magnet RM4 is connected through its in
terrupter springs and rm42 to a half-second
pulse supply causing the switch to advance one
45 step per pulse to positions 29, 30, 3| and then 32.
‘
10
In the next position of the switch, the cir
cuit for the relay FXY is maintained until relay
X releases andr‘connects ground at X2 to ter
minal ZG which is extended through contact
103 through the bank contact and wiper rm42 to 16
the magnet RM4‘ causing the wipers to advance _
to position 31.
In this position the circuit awaits
for a further Y pulse from the distant end which,
as already described, causes the operation of the
relay KB and Z and, at the termination of the
Y pulse, ground is connected over the terminal
MAG which advances the wipers of the switchv
R4 to position 38. In this position ground is ex
tended through rm_46, contacts pol, and terminal
X132 to the second winding of relay XB, Fig. 5,
which is operated thereby, and in parallel
through the metal recti?er, terminal X80 and
contacts k4 to relay FXY. The operation of
the relay FXY reconnects the Y frequency to
the trunk line. The operation of relay XB,
which looks up through contacts $113 and 22 to
ground, causes the operation of the magnet RM3
through contacts :23, 2| and :rb4. Relay XB also
closes at xbl, the circuit for relay X which in op
erating opens the short circuit across the inter
rupters ofRM3at m3 and causes the switch to
take a step. The switch R3 continues stepping
until the circuit is closed for the relay Z through
the bank contact and wiper rm32 and the con
tacts 1'4.
40
Relay Z in operating opens the circuit of the
magnet RM3, opens at 22 the holding circuit of
the relay KB and closes through the contacts
xl,‘a:b2 the circuit for RM4, which is therefore
caused to advance through both positions 38 and 45
In positions 28, 29, 30 and 3| relay FX is main
39 into position 40.
tained operated so that as a result the X fre
If the vrelay‘PC had been operated when the
switch reached position 38; via stl, rm3 I, rm2l .to
quency remains on the line the whole of this
period: In positions 32 and 33 the circuit for the
relay FX is open, but the circuit for the relay
-
FXY is closed so that in these two positions the
Y frequency is connected over the lines. The
interrupter circuit for the magnet RM4 is com
earth, because the switches R2 and R3 were in
phase, relays KB and FXY would not have op 50
erated, Y pulse would not have been connected
to the trunk line and relays CA, Fig. 9, and RC
would have been operated via J‘xyl, k5, pcl en
pleted wiper rm42 and the wipers are advanced
ergized, rm46 to earth.
55 to position 34. The toll line circuit now awaits
a signal from the distant end of Y frequency and
when this arrives, frequency-responsive relay Y
not shown connects ground through. contacts
b3, rcl, s02, Icll, wiper rm46, contact yl to the
60 terminal XZO, which is connected .to the direc
tion delay recorder shown in Fig. 5, through one
winding of relay KB and the relay Z, which both
operate.
7
Relay Z at 2| opens a possible circuit for the
65 magnet RM3, and contacts :cbl close the obvious
circuit of the relay X. When the Y pulse ter
minates, the relays KB and Z are both released.
The relay 163 is gauged with a heavy spring pres
sure so that it operates relatively slowly and re
70 leases quickly. The relay Z on the other hand
75
to advance a further step.
»
Relay RC is arranged to look over contacts 55
b2. Switch R4 returns home through contacts
102 and rm“ to ground. Relay RC indicates
that the toll ‘line circuit should receive an in
coming call and in consequence does not permit
the condition of- the group .test terminal to be 60
altered.
I
Assuming that the relay PC is not operated
and that the switch R4 was advanced to position
40, the circuit would again await the receipt of
Y pulse which again causes the operation of re
65
lays X8 and Z, and again at the termination of
the Y pulse the wipers advance to position 4|.
If the relay PC is still not operated the relays
KB and FXY will be again operated in posi
tions 4| and 42 and the wipers step forward to 70
has relatively light-pressure and operates quickly
and releases relatively slowly. During the pe
position »- 43 .
riod between relays KB and Z releasing, a cir
reconnect the Y pulse, the relays X3 and Z will
cuit is closed from ground, e2, :rl, :rb2, to the
terminal ‘MAG, which is connected via the cor
not operate but-the circuit will be completed from
' Assuming now that the distant end does not
the magnet .RM4 through the wiper rm42, con 75
7
2,112,549
tact k2, terminal MAG, 152, Fig. 5, .rl, make
before-break contacts mbl, left-hand winding of
the relay MA to ground.
Relay MA being of relatively high resistance,
the magnet RM4 will not be operated but the
relay MA will operate and close the contacts mal
and the half-second pulse supply to the second
winding of relay MA and the relay MB. When
this supply is connected the relay MB operates
and. the relay MA remains operated for the dura
tion of the pulse. On the completion of the
pulse, relay MB remains operated on its upper
winding through contacts ml)! in series with the
magnet RM4, but MA is released.
When
15 ground is again connected to the pulse supply
the circuit is completed through the contacts
mal, 717122 for the relay MC‘ and if by this time
Y pulse has not been received, relay MC operates
and connects ground via mcl, st4 to the MCG
20 terminal through contacts 106, Fig. 7, to the lower
winding of relay SC, which operates. Relay SC
closes at $03 a locking circuit through b2, rm“
to ground. Contacts s04 open the locking circuit
of relay C which in releasing closes a homing
25 circuit; RM4, interrupter, sci, cl, rm44, ground.
When the switch reaches home, ground is re
moved from the terminal AKI, and relay K is
released together with the direction delay
recorder.
30
35
It will be understood that the operation of
relay SC, indicating that the trunk line should
be used for an outgoing call, may take place at
position 40, 43, 46, etc. and similarly the opera
tion of the relay RC may take place at position
38, 4|, 44, etc.
If the trunk line circuit is associated with the
direction delay recorder on an outgoing connec
tion and the relay KW becomes operated because
the distant end recorder is associated with the
40 different trunk line, a circuit is completed
through contacts k‘! and g2 for the relay G, which
is arranged to lock up. The contacts gl and sub
sequently the contacts 93 and g4 advance the
wipers of the switch R4 through normal to posi
tion 26 in which position the circuit for the relay
45
G is opened. Relay G in releasing closes the
circuit for the magnet RM4 through 1'm42, 112, Q],
rm44 causing the switch to advance to position
El when reassociation with the direction delay
recorder will take place when the latter circuit
50
becomes available.
Considering now the case of an incoming call,
relays B and C of the trunk line circuit are op
erated and switch RM4 is advanced to position
55 2 but no further since SC is not energized.
It
remains in this position throughout the conversa
tion but on release a Y pulse is received from
the distant end.
Relay Y closes at 1/2 the circuit for the magnet
RM4 and switch R4 is advanced to» position 3.
ing positions, the controlling switch R3 is ad
vanced, and as soon as the switch R3 is in phase
with the switch R2, no further congestion “Y”
pulses are sent.
If no further Y pulse is received from the dis
tant exchange, relays MA, MB and MC are op
erated as already described. The subsequent op
eration of relay SC results in the trunk line being 10
made available for an outgoing call. If, on the
other hand, relay PC is operated resulting in the
operation of relay RC, the trunk line is prepared
to receive a call from the distant end.
It may be arranged that if the outgoing end 15
has no calls waiting the second signal sent in
positions 35 and 36 will be of X pulse rather than
of Y pulse; such an arrangement can be ac
cepted at the incoming end by wiring position 6
to position 9 through the back contact of a relay 20'
RX (not shown) responding to the X pulse. It
will be arranged that should the X pulse be re
ceived in position 6 the relay SC can be operated
immediately.
During the period when the trunk line is asso 25'
ciated with the direction delay recorder and relay
KY is operated, the possible circuit for the switch
R2 is opened at contact kyl and on this account
the circuit for the relay PC cannot be caused to
open instantaneously.
30
Reference has already been made to the fact
that in certain circumstances there may be a
preponderance of tra?ic in one direction and in
consequence over a relatively long period there
will be a large number of Waiting callsin one _'
direction. Under these conditions it may be di?i
cult for a call in the reverse direction to get
access. In order to eliminate this possibility a
compensator circuit is proposed as shown in Fig.
9.
It is the purpose of this circuit to vary the 40
connection via the bank contacts associated with
the wiper rm32 so that the size of the stages of
movement of said wipers, when sending con
gestion pulses, is in part dependent upon the
direction in which the majority of the traf?c is
flowing.
As an example, the contacts associated with
the wiper rm32 are divided up into three groups.
Contacts I, 3, 5, ‘I, 9 etc., are connected together
and wired to terminal CX. Contacts 2, 6, l0, l4, 50
etc. are connected together and; wired to terminal
CY, contacts 4, 8, l2, etc. are likewise connected
to terminal CZ, and also direct to the right-hand
winding of relay Z.
Relay CA, Fig. 9, is connected in series with 55
the operating winding of relays RC of the vari
ous trunk line circuits and every time that a
trunk line is released and assigned for an incom
ing call relay CA will operate. Relay CA closes
rm4l to terminal AKZ to cause the association
the obvious circuit for the switch R5 which is 60
caused to take one step for each successive junc
tion assigned for incoming use.
'_
with the direction delay recorder to take place.
When the Y pulse is completed and the relay K
wiper rm5l are commoned together and con
operated, ground‘is connected through 1/3, Icl, and
nected to the terminal CZ. ' Corresponding con
In position 3 ground is connected through wiper
rmlll to advance the switch to position 4.
In this position the relay FXY is operated and
the return Y pulse is sent to the distant trunk
exchange. The wipers are advanced by direct
earth on 111241 to position 6 where a. further Y
pulse signal is expected from the other exchange
Contacts 3, 4, 5, 6, ‘I, B, 9, I0 associated with
nected to terminal CY and contacts 4, 5,‘ 6, 1, 8,
9, l0 associated with wiper rm53 are connected
to the terminal CX.
,
On the second successive incoming call switch 70
R5 reaches position No. 3 and the terminals CY
and CZ are commoned together and because of
relay X13 and Z, Fig. 5, in the manner already
this the relay Z in the direction delay recorder is
operated after only two steps instead of four
'
In positions ‘I and 8 the operation of relay X5
65
tacts associated with the wiper rm52 are con
and when it is received causes the operation of
described.
75
is made dependent on the condition of contacts
pol as before so that, in this and subsequent sen-d
steps of R3.
"
~
8
2,1 12, 54,9;
If ‘a ‘further incoming‘call is received, R5 ad
vances another step and in this .position terminals
CX, CY and CZ are all commoned together. Re
lay Z operates after every one step of R3. On
the use of any junction in' the route for an out
means at both o?ices responsive to a trunk cir
drive the switch to a further home position, from
whence the process will be repeated.
wherethe greater traffic congestion exists that
the free trunk circuit is to be used on an out
'
going call .and :for indicating at the other o?ice
that the free trunk circuit is to be reserved for an
rality of link circuits each-comprising a ?nder,
incoming call.
atively associating any link with any position,
means responsive to the existence of a calling
condition on any line of said incoming line group
for operating any idle link to connect its asso
20 ciated ?nder with said calling line, and means
responsive to an operation at anyone of said
7. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said 15
offices, switching means at each o?ice for seizing
idle trunk circuits, means at each o?ice for re
cording during periods when no idle trunk cir
cuit is available the aggregate Waiting time of
calls awaiting an idle trunk circuit, means at 20
each o?ice operative when a trunk circuit be
comes available for transmitting signal impulses
the link extended to the calling line with the
to the other o?‘ice, and means at each o?ice joint
ly responsive to the recording means of that office
and to the impulses received from the other o?ice 25
for allocating said idle trunk circuit for an out
going call to the use of the office in which the
2. In a toll switching system, the combination
of two of?ces connected by a plurality of two-way
trunk lines, a selector circuit at each o?ice having
access to said trunk lines, means at each o?ice
operatively associated with each selector for de
30 termining and recording the time interval during
which all of said trunk lines are busy, means
at each o?ice operatively associated with each
selector for determining and recording the time
interval during which each of said selectors has
35 been 'waiting for a free trunk line to establish a
call in its own direction, means responsive to a
line becoming free for signaling over said line
the selector delay at each oflice, and means for
allotting said free line to the o?‘ice which had the
longest selector delay.
3. In a telephone system, two o?ices, a group of
two-way trunk‘ circuits extending between said
o?ices, switching means at each office for seizing
idle trunk circuits,'and means at each o?ice con
45 trollable in accordance with the number of calls
awaiting completion at each oilice and the aggre
gate waiting period of such calls for allocating an
idle trunk circuit for the use of the o?ice in which
the tra?ic congestion is greater.
4. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said
o?‘ices, switching means at each o?ice for seizing
idle trunk circuits, means at each o?ice for ‘re
cording during periods when no idle trunk cir
55 cuits are available the aggregate waiting time of
calls awaiting an idle trunk circuit, and means
at each o?ice controllable jointly by the recording
means at both o?ices for determining whichfof?ce
60
10
positions for operating said allotter to associate
position at which said operation has taken place.
50
cuit becoming free for indicating at the oi?ce
1. In a toll switching system, the combination
with a plurality of operators’ positions of a plu
an incoming line group available for connection
15 with all of said link circuits, an allotter for oper
40
idle trunk circuits, means at each office ‘for, re
cording during periods when no idle trunk cir
cuits are available the aggregate waiting time.
of calls awaiting an idle trunk circuit, and means
at each o?ice controllable jointly by the recording
going call a relay MC (not shown) will operate
and complete the circuit through wiper rm54 to
What is claimed is:
25
o?ices, switching means at each'o?ice for seizing
may use an idle trunk circuit for an outgoing
call when it becomes free.
'
5. In a telephone system, two o?icesra group
of two-way trunk circuits extending between said
o'?ices, switching means at each o?icev for seiz
ing idle trunk circuits, means at each o?ice for
65
recording during periods when no idle trunk cir
cuits are available the aggregate waiting time of
calls awaiting an idle trunk circuit, and means
at each office controllable jointly by the record
70 ing' means at both o?ices for allocating a trunk
circuit when it becomes idle to the use of the o?ice
whose; recording means indicates the greater
trai'?c congestion.
.6. In a telephone system, ‘two o?ices, a group of '
7.5 two-way trunk circuits extending between said
traffic congestion is greater.
8. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said 30
o?ices, switching means at each o?ice for seizing
idle trunk circuits, means at each o?ice for re
cording during periods when no idle trunk cir
cuits are available the aggregate waiting time of
calls awaiting an idle trunk circuit, means at each '
o?ice operative when a trunk circuit becomes
available for transmitting signal impulses in
alternation over said idle trunk circuit to the
other o?ice, and means at each office jointly re
sponsive to the recording means of that o?ice 40
and to the impulses received from the other o?ice
for allocating said idle trunk circuit for an out
going call from the o?ice in which the tra?ic
congestion is ‘greater and for an incoming call
at'the office in which the tra?ic congestion is less. 45
9, In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said
o?ices, switching means at each o?ice for seizing
idle trunk circuits, a ?rst recording switch at each
o?ice, means at each office operable during periods 50
when no idle trunk circuits are available for set
ting the associated recording switch in accord
ance with the aggregate waiting time of calls
awaiting an idle trunk circuit, a second recording
switch at each office, means at each o?ice opera 55
tivewhen a trunk circuit becomes free for trans
mitting signal impulses to the other office for set
ting the second v recording switch at the other
o?ice, and means operative when the recording
switches of either o?ice are in substantial phase 60
relationship for‘ transmitting a signal to the other
o?ice indicative that the free trunk circuit may be
used at such o?ice for an outgoing call.
10. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said 65
of?ces, switching means at each o?ice for seizing
idle trunk circuits, a ?rst recording switch at each
o?ice, means at each o?ice operable during periods
when no idle trunk circuits are available for set
ting the associated recording switch in accordance
with the aggregate waiting’ time of calls awaiting
an idle trunk circuit, a second recording switch
at each office, means at each o?ice operative when
atrunk circuit'becomes free for transmitting sig 75.
9
2,112,549
nal impulses to the other o?ice for advancing the
second recording switch at the other o?ice a pre
determined amount in response to each impulse,
means operative when the recording switches of
either office are in substantial phase relationship
for transmitting a signal to the other o?ice indica
tive that the free trunk circuit may be used at
said other of?ce for an outgoing call, and means
at each of?ce effective when the other o?ice has
10 been given precedence for a predetermined num
ber of successive outgoing calls for reducing the
amount of advancement of the second recording
switch thereof in response to impulses from the
other oi?ce whereby said o?ice is given precedence
15 for completing an outgoing call.
11. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said
o?ices, switching means at each oi?ce for seizing
idle trunk circuits, a ?rst recording switch at each
20 o?ice, means at each o?ice operable during periods
when no idle trunk circuits are available for set
ting the associated recording switch in accordance
with the aggregate waiting time of calls awaiting
an idle trunk circuit, a second recording switch
25 at each oi?ce, means at each o?ice operative when
13. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said
o?ices, switching means at each omce for seizing
idle trunk circuits, traf?c congestion recording
means in each of?ce, and means in each of?ce
operative in response to two trunk circuits be
coming available substantially simultaneously for
associating the recording means of each of said
o?ices with the opposite ends of one of said avail
able trunk circuits.
10
14. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said
o?ices, switching means at each office for seizing
idle trunk circuits, means "at each office for re
cording during periods when no idle trunk cir 15
cuit is available the aggregate waiting time of
calls awaiting an idle trunk circuit, means at
each end of each trunk circuit individual thereto
operative when a trunk circuit becomes available
for transmitting signal impulses over said trunk 20
circuit to the other office, and means at each
office jointly responsive to the recording means
of that of?ce and to the impulses received from
the other o?ice for allocating said idle trunk cir
cuit for an outgoing call to the use of the office 25
a trunk circuit becomes free for transmitting sig
in which the traffic congestion is greater.
nal impulses to the other of?ce for advancing the
15. In a telephone system, two o?‘ices, a group
of two-way trunk circuits extending between said
offices, switching means at each o?ice for seizing
idle trunk circuits, a tra?c congestion recorder
second recording switch at the other o?ice a pre
determined amount in response to each impulse,
30 means operative when the recording switches of
either office are in substantial phase relationship
for transmitting a signal to the other of?ce indica
tive that the free trunk circuit may be used at
said other office for an outgoing call, and means
35 at each office e?ective in response to the allotment
in succession of di?erent predetermined numbers
of available trunk circuits to the other oilice for
outgoing calls for successively reducing the
amount of advancement of the second recording
switch thereof in response to the impulses from
the other office whereby said office is given prec
edence for completing an outgoing call.
12. In a telephone system, two o?ices, a group
of two-way trunk circuits extending between said
45 o??ces, switching means at each omce for seizing
idle trunk circuits, tra?ic congestion recording
means in each of?ce, and means in each office
operative in response to a trunk circuit becoming
available for associating the recording means of
50 each of said o?ices with the opposite ends of said
available trunk circuit,
in each of?ce, said recorders each comprising a
?rst recording switch operable during periods
when no idle trunk circuits are available for
recording the aggregate ' waiting time of calls
awaiting an idle trunk circuit, and a second re 35
cording switch, means at each end of each trunk
circuit individual theretoand operative when a
trunk circuit becomes available for associating the
end of said trunk circuit at each oflice with the
tra?ic congestion recorder thereat and for trans 40
mitting signal impulses to the other oi?ce for set
ting the second recording switch at the other
o?ice, and means operative when the recording
switches of either o?ice are in substantial phase
relationship for transmitting a signal to the other 45
office indicative that the free trunk circuit may be
used at said other office for an outgoing call.
ESMOND P. G. WRIGHT.
GEORGE C,
50
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